In Chapter 7, E-mail and Notification, we looked at mail handlers, which are used by JIRA to periodically poll mailboxes and create issues. Mail handler is an example of a feature in JIRA called Services.
A service is something that is run periodically by JIRA, performing a certain function. They are equivalent to that of a cron job in Unix or scheduled job in Windows. A mail handler for example, is a service that creates issues from e-mails pulled from the mail inbox. There are other services used by JIRA, such as the Mail Queue Service which flushes out notification e-mails. Services are a great way to set up some automated jobs in JIRA and are often used to integrate JIRA with other systems by constantly polling and sending information between the two.
JIRA comes with a list of useful services that you can install out of the box, but if you want to have services to perform specialized functions, you will need the help of plugins, which will be covered in the next section.